Hard Stop Homing allows you to home an axis with excellent precision by simply driving the axis into a hard mechanical stop at a moderate speed. This is how it works:
Let’s say that you have an axis that is 100,000 counts long. You simply make a moderate-speed move of 100,100 counts toward a mechanical stop. At some point during the move the axis will contact the mechanical stop. At that point the SST will automatically sense the hard stop and fold back the torque/force to a user-defined level and ignore further pulses in that direction. Any subsequent pulses in the other direction (away from the mechanical stop) will be responded to as usual. So after the completion of the 100,100 count move you simply command the axis to move away from the mechanical stop by a fixed amount to a precision home position (typically repeatable to within one encoder count).
This is another proprietary feature of the SST servo drive that allows you to lower costs and increase system reliability within your machine.
As you can see, this can eliminate the costs for home or limit sensors and eliminates the cost of hardware/software to process encoder signals for the homing operation. Mechanical alignment of home switches and software offset calibrations are also eliminated. Because of this, the control software is simplified, reducing development time.
Calibration efforts during manufacturing are reduced using the Hard Stop Homing feature since sensor alignment, index mark alignment, and/or software offsets are not necessary.
Some stepper motor driven axes use this method to home an axis (the motor just stalls when the stop is encountered) so this feature allows the drop-in replacement of a servo in these applications without changing the control software or adding sensors. When this mode of operation is used with a stepper motor the accuracy is only guaranteed to within 4 full steps (not micro-steps) and the homing operation as the motor stalls is noisy. When using the SST servo drive’s Hard Stop Homing feature, the accuracy is typically within an encoder count and the operation is silent.
The Hard Stop Homing feature (together with the RAS, Torque Fold-back modes, MoveDone output and flexible input resolution) helps enable the use of low cost controls, that lack encoder feedback inputs, even in machines that require state-of-the-art performance.